1. Field of the Invention
This invention relates generally to laser communication systems and methods and more particularly to duplex free-space laser communication systems and methods.
2. Description of the Related Art
Random variations in the refractive index, commonly referred to as atmospheric or optical turbulence, significantly limit the performance of free-space laser communication systems. Optical turbulence-induced random phase and intensity fluctuations (scintillations) across the received wave-front lead to intensity fading at the receiver, with the result being increased system bit error rates. Attempts have been made at applying some type of adaptive optics correction scheme to reduce the effects of optical turbulence on free-space laser communication systems. Adaptive optical systems that have previously been used for free-space laser communication require direct measurement of the wave-front phase using wave-front sensors such as a Shack-Hartmann sensor or shearing interferometer, followed by some type of wave-front reconstruction and conjugation. Disadvantageously however, in the presence of the strong phase and intensity fluctuations characteristic of near-earth propagation paths, these types of systems perform poorly.